The present invention relates to seals for the pressure cushions of double belt presses.
Double belt presses are employed in material laminating and compression procedures in which a strip of material to be compressed is fed between two traveling metal belts which press against opposite surfaces of the material in order to compress it. Such presses are composed essentially of two metal belts each mounted on a respective support structure and between which a compression region is formed. The belts are advanced around their respective support structures so as to convey the material being worked upon through the press as that material is being pressed.
One known type of double belt press is constructed to operate according to the pressure cushion principle. For this purpose, the support structure associated with each belt is provided with a pressure plate located behind the belt in the compression region and provided with a slide surface seal forming a frame which encloses a pressure cushion formed by a liquid or gaseous pressure medium. The major faces of the cushion are bounded by the surface of the pressure plate and the rear surface of the associated metal belt, and the slide surface seal cooperates with the pressure plate and the rear belt surface in order to seal the region containing the pressure medium. The pressure medium acts against the rear surface of the associated metal belt to press it against the work material.
Slide surface seals for such structures must be designed in such a manner as to assure that friction forces occurring between the rear surface of the metal belt, which is generally of steel, and the seal are dependably directed into the associated pressure plate of the support structure of the machine without inducing changes in the shape of the seal. In addition, the heat developed as a result of friction should be transmitted to the associated pressure plate as completely as possible, i.e. without creating any significant temperature differential in the seal itself, and discharge of pressure medium from the cushion should be reliably prevented, except for passage of a minimum quantity to provide lubrication of the seal surfaces.
Known seals of this type, a typical example of which is disclosed in German Pat. No. 2,722,197, have been found to possess a number of drawbacks, among which are their high manufacturing cost and poor heat conductance characteristics, which result in accumulation of heat by the sealing material.